Acid Stain is not a paint or a coating agent. Rather, it's a coloring process involving a chemical reaction that occurs upon application on cement. A solution made with water, acid and inorganic salts reacts with minerals already present in the concrete. The result of this reaction is color. It works extremely well on new or old concrete surfaces. Acid Stain is a very durable product if properly protected with sealer or wax. It can be applied both to interior and exterior areas.